The API Framework

“Above” the graphics layer is the place where all applications that can run on an operating system can work together: the application program interface (API). You can extend the workbench metaphor used to describe system memory to the API: if the workbench is the memory, then the API is the collection of tools that the application needs to get work done.

When a developer writes an application, he or she does not have to write every single instruction that is necessary to, say, open a window on the screen. If every trivial function required intricate instructions, all applications would have trillions of lines of code and would be too big for the average computer to handle.